The present invention relates to automatic transmission systems and, more particularly to an improved pressure regulator valve for General Motors 4L80E automatic transmissions (hereinafter “GM transmissions”) dating from 1999 to the present.
Automatic transmission systems of the prior art have a hydraulic circuit sub-system which includes at least a hydraulic pump, a valve body having fluid conducting passages or circuits, input and exhaust ports formed within the fluid circuits, and a plurality of spool valves so-called because of their resemblance to sewing thread type spools. Such valves are comprised of cylindrical pistons having control diameters or spools formed thereon, which alternately open and close the ports to regulate the flow and pressure of automatic transmission fluid (hereinafter “ATF”) within the fluid circuits to actuate various components of the transmission. It will be understood that in describing hydraulic fluid circuits, ATF usually changes names when it passes through an orifice or control valve in a specific circuit.
Pumps in automatic transmission systems are generally positive displacement pumps driven by the engine of the vehicle wherein the transmission is installed. A positive displacement pump is one, which has the same output per revolution regardless of pump speed or pressure already developed in the system. Thus, it is necessary to regulate ATF pressure so it does not get too high and damage other components. In the GM transmissions a pressure regulator valve employs a piston and a spring that compresses at a specific pressure to allow some ATF to flow back to the pump reservoir or sump bypassing the hydraulic circuit and reducing pressure. By using a pressure regulator valve with a compression spring calibrated to a pressure lower than the pump's output, a constant ATF pressure can be maintained in the hydraulic system during operation.
When the engine of the vehicle is turned off, ATF contained within the torque converter during operation gradually drains back to the fluid sump. At initial engine start-up this can result in an insufficient fluid level in the torque converter to operate the vehicle. In addition, the original equipment manufacture (hereinafter “OEM”) pressure regulator valve in the GM transmissions does not send sufficient line pressure from the pump output circuit into the torque converter charge circuit in the Park gear range or at idle speed to refill the torque converter to permit instant operation of the vehicle at engine start-up.